DNA encoding hydantoinase, DNA encoding N-carbamyl-L-amino acid hydrolase, recombinant DNA, transformed cell, method of producing protein, and method of producing optically active amino acid

ABSTRACT

The present invention provides a method of producing optically active amino acids from 5-substituted hydantoin by isolating a hydantoinase gene and an N-carbamyl-L-amino acid hydrolase gene involved in an ability to convert 5-substituted hydantoin or N-carbamylamino acid into optically active amino acids from a microorganism of the genus  Microbacterium  having the above ability and by improving gene amplification and transcriptional and translational activities thereby preparing a recombinant wherein the amount of the desired enzymes produced is increased. The hydantoinase gene is, for example, a DNA encoding for a protein having a hydantoinase activity, which has the nucleotide sequence of SEQ ID NO:1. The N-carbamyl-L-amino acid hydrolase gene is, for example, a DNA encoding for a protein having an N-carbamyl-L-amino acid hydrolase activity, which has the nucleotide sequence of SEQ ID NO:3.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. Ser. No. 11/476,572, filed on Jun. 29, 2006, now U.S. Pat. No. 7,361,490, which is a divisional of U.S. Ser. No. 10/289,360, filed on Nov. 7, 2002, now U.S. Pat. No. 7,098,020, which is a continuation of PCT/JP02/02173, filed on Mar. 8, 2002, which claims priority to JP 2001-065814, filed on Mar. 8, 2001, and JP 2001-298619, filed on Sep. 27, 2001.

TECHNICAL FIELD

The present invention relates to a DNA encoding hydantoinase and a DNA encoding N-carbamyl-L-amino acid hydrolase and in particular to a DNA encoding hydantoinase, a DNA encoding N-carbamyl-L-amino acid hydrolase, a recombinant DNA, a transformed cell, a method of producing a protein and a method of producing optically active amino acids, which can be used preferably in production of optically active amino acids represented by L-tyrosine.

BACKGROUND ART

As one of methods for producing amino acids by use of an enzyme, a method of asymmetric decomposition of chemically inexpensively synthesized 5-substituted hydantoin compounds as the starting material into optically active amino acids is known. This method of producing optically active amino acids from 5-substituted hydantoin compounds is important for production of pharmaceutical preparations, products in chemical industry, food additives etc.

In this method of producing amino acids from 5-substituted hydantoin compounds, the following enzymes (1) and (2) are necessary.

(1) An enzyme (hydantoinase) of catalyzing the reaction of forming N-carbamylamino acid by acting on a 5-substituted hydantoin compound to hydrolyze the compound.

(2) An enzyme (N-carbamylamino acid hydrolase) of catalyzing the reaction of forming an optically active amino acid by acting on the formed N-carbamylamino acid to hydrolyze the compound.

For producing optically active amino acids from 5-substituted hydantoin compounds, (1) hydantoinase and/or (2) N-carbamylamino acid hydrolase must be an optically selective enzyme, and a method of using a microbial enzyme system and a method of combining a microbial enzyme system with a chemical reaction system have been known.

For example, the known method of producing D-amino acids by a D-amino acid-producing microorganism or by enzyme-containing materials produced by the microorganism includes a method of using a microorganism of the genus Pseudomonas (Japanese Patent Application Publication No. 56-003034), a method of using a microorganism of the genus Agrobacterium (Japanese Patent Application Laid-Open No. 03-019696) etc. In these D-amino acid-producing microorganisms, their hydantoinase activity is generally often specific to D-5-substituted hydantoin, and when DL-5-substituted hydantoin is used as the starting material, only the D-hydantoin is hydrolyzed to form N-carbamyl-D-amino acid, which is further hydrolyzed to finally give D-amino acid only, as shown in the following reaction scheme (I).

D-Amino Acid-Producing Microorganism

As the method of producing L-amino acids by an L-amino acid-producing microorganism or by enzyme-containing materials produced by the microorganism, there are reports on a method of using a microorganism of the genus Flavobacterium (Japanese Patent Application Publication No. 54-008749), a method of using a microorganism of the genus Bacillus (Japanese Patent Application Laid-Open No. 63-024895), a method of using a microorganism of the genus Pseudomonas (Japanese Patent Application Laid-Open No. 1-071476) and a method of using a microorganism of the genus Arthrobacter (J. Biotechnol. 46, 63, 1996) etc. In these L-amino acid-producing microorganisms, their N-carbamylamino acid hydrolase activity is often specific to L-amino acids. Accordingly, when DL-5-substituted hydantoin is used as the starting material, both D- and L-hydantoin is hydrolyzed to give N-carbamyl-DL-amino acids, out of which the N-carbamyl-L-amino acid is selectively hydrolyzed by the N-carbamylamino acid hydrolase, to finally give the L-amino acid only, as shown in the following reaction scheme (II).

L-Amino Acid-Producing Microorganism

From a microorganism of the genus Flavobacterium out of the L-amino acid-producing microorganisms mentioned above, hydantoinase and N-carbamylamino acid hydrolase are partially purified, and the hydantoinase is known to be able to act on both D- and L-configurations of 5-substituted hydantoin compounds (Agric. Biol. Chem., 51, 737 (1987)).

However, because the above enzyme preparation is obtained by partial purification, whether the action of the enzyme preparation is attributable to the single enzyme or not is unclear, and the amino acid sequence of the hydantoinase derived from Flavobacterium and the nucleotide sequence of its encoding gene are not revealed.

From a microorganism of the genus Arthrobacter, on one hand, a hydantoinase gene and N-carbamylamino acid hydrolase gene have been isolated, and it is known that L-amino acids can be produced by a recombinant prepared using the genes. However, the hydantoinase derived from a microorganism of the genus Arthrobacter does not act on DL-5-(4-hydroxybenzyl) hydantoin, and can thus not be used for production of L-tyrosine from DL-5-(4-hydroxybenzyl) hydantoin.

DISCLOSURE OF THE INVENTION

For efficient production of optically active amino acids, it is preferable to use a recombinant producing enzymes hydantoinase and N-carbamylamino acid hydrolase in higher amounts by isolating their genes, amplifying the genes and improving transcriptional and translational activity. However, there is no report on isolation of hydantoinase acting on DL-5-(4-hydroxybenzyl) hydantoin as a starting material for tyrosine, so there is a problem that hydantoinase widely available for synthesis of optically active amino acids represented by L-tyrosine cannot be produced efficiently by preparing a recombinant.

The cultured L-amino acid-producing microorganisms can be used to produce optically active amino acids from 5-substituted hydantoin compounds, but in this case, there are problems such as necessity for use of inducers such as hydantoin derivatives or use of a large amount of the cultured microorganisms in order to increase the amount of the enzymes.

Accordingly, the object of the present invention is to provide a method of efficiently producing optically active amino acids represented by L-tyrosine from 5-substituted hydantoin represented by 5-(4-hydroxybenzyl) hydantoin by isolating a hydantoinase gene and N-carbamylamino acid hydrolase gene from a microorganism having an ability to convert 5-(4-hydroxybenzyl) hydantoin into L-tyrosine to reveal the amino acid sequences of the enzymes and the nucleotide sequences of genes encoding therefor, and preparing a recombinant wherein the amount of the enzymes produced is increased to produce optically active amino acids efficiently.

As a result of extensive study in view of the problems described above, the present inventors successfully isolated a hydantoinase gene and N-carbamyl amino acid hydrolase gene from a microorganism having an ability to convert 5-(4-hydroxybenzyl) hydantoin into L-tyrosine, arriving at the present invention.

The present invention has following 32 characteristics:

(1) A DNA encoding for a protein having a hydantoinase activity, which has the following nucleotide sequence (a) or (b):

-   -   (a) the nucleotide sequence set forth in SEQ ID NO:1 in the         Sequence Listing, and     -   (b) a nucleotide sequence hybridizing under stringent conditions         with DNA consisting of a nucleotide sequence complementary to         the nucleotide sequence set forth in SEQ ID NO:1 in the Sequence         Listing.

(2) A DNA encoding for a protein having a hydantoinase activity and having the following amino acid sequence (c) or (d):

-   -   (c) the amino acid sequence set forth in SEQ ID NO:2 in the         Sequence Listing, and     -   (d) an amino acid sequence wherein in the amino acid sequence         set forth in SEQ ID NO:2 in the Sequence Listing, one or several         amino acid residues are replaced, deleted, inserted, added or         inverted.

(3) A recombinant DNA obtained by linking the DNA according to the item (1) or (2) to a vector DNA.

(4) The recombinant DNA according to the item (3), wherein the vector DNA is a pUC series plasmid, a pBR322 series plasmid, or a plasmid derived from derivatives thereof.

(5) A cell transformed with the recombinant DNA according to the item (3) or (4).

(6) The cell according to the item (5), wherein the cell is derived from Escherichia coli.

(7) A method of producing a protein having a hydantoinase activity, wherein the cell according to the item (5) or (6) is cultured in a medium, and a protein having a hydantoinase activity is accumulated in the medium and/or the cells.

(8) A protein having a hydantoinase activity, which has the following amino acid sequence (c) or (d):

-   -   (c) the amino acid sequence set forth in SEQ ID NO:2 in the         Sequence Listing, and     -   (d) the amino acid sequence wherein in the amino acid sequence         set forth in SEQ ID NO:2 in the Sequence Listing, one or several         amino acid residues are replaced, deleted, inserted, added or         inverted.

(9) The protein according to the item (8), wherein the protein acts on at least DL-5-(4-hydroxybenzyl) hydantoin.

(10) A method of producing N-carbamylamino acids, comprising a process for producing a protein having a hydantoinase activity by the method according to the item (7) and a process for producing N-carbamylamino acids by allowing the protein having a hydantoinase activity to act on 5-substituted hydantoin.

(11) A method of producing optically active amino acids, comprising a process for producing a protein having a hydantoinase activity by the method according to the item (7) and a process for producing optically active amino acids by allowing the protein having a hydantoinase activity and an enzyme optico-selectively hydrolyzing N-carbamylamino acids or a material containing the enzyme to act on 5-substituted hydantoin.

(12) A method of producing optically active tyrosine, comprising a process for producing a protein having a hydantoinase activity by the method according to the item (7) and a process for producing optically active tyrosine by allowing the protein having a hydantoinase activity and an enzyme optico-selectively hydrolyzing N-carbamylamino acids or a material containing the enzyme to act on DL-5-(4-hydroxybenzyl) hydantoin.

(13) A DNA encoding for a protein having an N-carbamyl-L-amino acid hydrolase activity, which has the following nucleotide sequence (a) or (b):

-   -   (a) the nucleotide sequence set forth in SEQ ID NO:3 in the         Sequence Listing, and     -   (b) the nucleotide sequence hybridizing under stringent         conditions with DNA consisting of a nucleotide sequence         complementary to the nucleotide sequence set forth in SEQ ID         NO:3 in the Sequence Listing.

(14) A DNA encoding for a protein having an N-carbamyl-L-amino acid hydrolase activity and having the following amino acid sequence (c) or (d):

-   -   (c) the amino acid sequence set forth in SEQ ID NO:4 in the         Sequence Listing, and     -   (d) the amino acid sequence wherein in the amino acid sequence         set forth in SEQ ID NO:4 in the Sequence Listing, one or several         amino acid residues are replaced, deleted, inserted, added or         inverted.

(15) A recombinant DNA obtained by linking the DNA according to the item (13) or (14) to a vector DNA.

(16) The recombinant DNA according to the item (15), wherein the vector DNA is a pUC series plasmid, a pBR322 series plasmid, or a plasmid derived from derivatives thereof.

(17) A cell trans formed with the recombinant DNA according to the item (15) or (16).

(18) A cell according to the item (17), wherein the cells are derived from Escherichia coli.

(19) A method of producing a protein having an N-carbamyl-L-amino acid hydrolase activity, wherein the cell according to the item (17) or (18) is cultured in a medium, and a protein having an N-carbamyl-L-amino acid hydrolase activity is accumulated in the medium and/or the cells.

(20) A protein having an N-carbamyl-L-amino acid hydrolase activity, which has the following amino acid sequence (c) or (d):

-   -   (c) the amino acid sequence set forth in SEQ ID NO:4 in the         Sequence Listing, and     -   (d) the amino acid sequence wherein in the amino acid sequence         set forth in SEQ ID NO:4 in the Sequence Listing, one or several         amino acid residues are replaced, deleted, inserted, added or         inverted.

(21) A method of producing L-amino acids, comprising a process for producing a protein having an N-carbamyl-L-amino acid hydrolase activity by the method according to the item (19) and a process for producing L-amino acids by allowing the protein having an N-carbamyl-L-amino acid hydrolase activity to act on N-carbamyl-L-amino acids.

(22) A method of producing L-amino acids, comprising a process for producing a protein having an N-carbamyl-L-amino acid hydrolase activity by the method according to the item (19) and a process for producing L-amino acids by allowing the protein having an N-carbamyl-L-amino acid hydrolase activity and an enzyme hydrolyzing 5-substituted hydantoin or a material containing the enzyme to act on 5-substituted hydantoin.

(23) A method of producing L-amino acids, comprising a process for producing a protein having a hydantoinase activity by the method according to the item (7), a process for producing a protein having an N-carbamyl-L-amino acid hydrolase activity by the method according to the item (19), and a process for producing L-amino acids by allowing the protein having a hydantoinase activity and the protein having an N-carbamyl-L-amino acid hydrolase activity to act on 5-substituted hydantoin.

(24) A method of producing L-tyrosine, comprising a process for producing a protein having a hydantoinase activity by the method according to the item (7), a process for producing a protein having an N-carbamyl-L-amino acid hydrolase activity by the method according to the item (19), and a process for producing L-tyrosine by allowing the protein having a hydantoinase activity and the protein having an N-carbamyl-L-amino acid hydrolase activity to act on DL-5-(4-hydroxybenzyl) hydantoin.

(25) A method of producing optically active N-carbamylamino acids, comprising recovering optically active amino acids produced by the method according to any of the items (11), (12) and (22) to (24).

(26) A method of producing optically active amino acids, comprising chemically or enzymatically converting optically active N-carbamylamino acids produced by the method according to the item (25) into amino acids.

(27) A structural gene group encoding for proteins involved in production of L-amino acids, which has the following nucleotide sequence (a) or (b):

-   -   (a) the nucleotide sequence set forth in SEQ ID NO:5 in the         Sequence Listing, and     -   (b) the nucleotide sequence hybridizing under stringent         conditions with DNA consisting of a nucleotide sequence         complementary to the nucleotide sequence set forth in SEQ ID         NO:5 in the Sequence Listing.

(28) A recombinant DNA obtained by linking the DNA according to the item (27) to a vector DNA.

(29) A cell transformed with the recombinant DNA according to the item (28).

(30) A method of producing a hybrid protein involved in production of L-amino acids, wherein a cell according to the item (29) is cultured in a medium, a hybrid protein involved in production of L-amino acids are accumulated in the medium and/or the cells, and the hybrid protein is recovered.

(31) A method of producing optically active amino acids, comprising a process for producing a hybrid protein involved in production of L-amino acids by the method according to the item (30) and a process of allowing the hybrid protein involved in production of L-amino acids to act on 5-substituted hydantoin.

(32) A method of producing optically active tyrosine, comprising a process for producing a hybrid protein involved in production of L-amino acids by the method according to the item (30) and a process of allowing the hybrid protein involved in production of L-amino acids to act on DL-5-(4-hydroxybenzyl) hydantoin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram which shows the structure of a structural gene group encoding for hydantoin racemase, hydantoinase and N-carbamyl-L-amino acid hydrolase, respectively; and

FIG. 2 is a flowchart which shows the process of producing hydantoinase and N-carbamyl-L-amino acid hydrolase according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention are explained in detail below while referring to the accompanying diagrams. An explanation about the invention will be given in the following order:

[I] DNA encoding for a protein having a hydantoinase activity and a protein having an N-carbamyl-L-amino acid hydrolase activity,

[II] Method of producing a protein having a hydantoinase activity and a protein having an N-carbamyl-L-amino acid hydrolase activity, and

[III] Method of producing an optically active amino acid.

In this specification, the protein having a hydantoinase activity is also referred to as hydantoinase, and the protein having an N-carbamylamino acid hydrolase activity is also referred to as N-carbamylamino acid hydrolase.

[I] DNA Encoding Hydantoinase and N-carbamyl-L-amino Acid Hydrolase

The DNA encoding hydantoinase and N-carbamyl-L-amino acid hydrolase according to the present invention was obtained in a process of study on hydantoin racemase and its DNA in Aureobacterium liquefaciens AJ3912 (FERM-P3133) described in Japanese Patent Application No. 2000-278571. Flavobacterium sp. AJ3912 (FERM-P3133) was initially deposited on Jun. 27, 1975 with the National Institute of Bioscience and Human-Technology, the Agency of Industrial Science of Technology, the Ministry of International Trade and Industry, Japan (at present, International Patent Organism Depositary (IPOD), National Institute of Advanced Industrial Science and Technology (AIST) (ChuoNo. 6, Higashi 1-1-1, Tsukuba City, Ibaraki Pref., JP, 305-8566)), but it was revealed as a result of re-identification that this microorganism is classified into Aureobacterium liquefaciens. At present, the species of this microorganism is changed from Aureobacterium liquefaciens to Microbacterium liquefaciens, and the microorganism is deposited as Microbacterium liquefaciens AJ3912 (National Deposition No. FERM-P3133 and International Deposition No. FERM BP-7643, transferred on Jun. 27, 2001 under the International Deposition) with International Patent Organism Depositary (IPOD), National Institute of Advanced Industrial Science and Technology (AIST) (ChuoNo. 6, Higashi 1-1-1, Tsukuba City, Ibaraki Pref., JP, 305-8566).

The physiological properties of Microbacterium liquefaciens AJ3912 (FERM-P3133) were examined in light of a microbial classification book, Berjey's [phonetic transcription] Manual of Determinative Bacteriology, Vol. 1 (9th edition, 1994, William & Wilkins Publishing Company), and the test results are shown in Table 1.

TABLE 1 Results of re-identification of Microbacterium liquefaciens AJ3912 Gram stainability positive Form of cells bacillus-shaped Motility none Nitrate reduction − Pyrimidinase − Pyridonyl allyl amidase − Alkali phosphatase + β-Glucuronidase − β-Galactosidase + α-Glucosidase + N-Acetyl-β-glucosaminidase + Aesculin (glucosidase) + Urease − Gelatin liquefaction + Fermentability of hydrocarbons  glucose −  ribose −  xylose −  mannitol −  maltose −  lactose −  Saccharose −  glycogen − Anaerobic growth − Casein hydrolyzability +

The present inventors estimated that in isolation of a hydantoin racemase gene from Aureobacterium liquefaciens AJ3912 (FERM-P3133) as described in Japanese Patent Application No. 2000-278571, a simultaneously obtained nucleotide sequence downstream from the hydantoin racemase gene is a part of a hydantoinase gene, and this DNA fragment was amplified by the PCR method and utilized as the probe by which the full-length hydantoinase gene could be successfully isolated and obtained from a gene library of the bacterial strain. Similarly, the present inventors estimated that in isolation of the hydantoinase gene of the present invention, a nucleotide sequence downstream from the hydantoinase gene is a part of an N-carbamyl-L-amino acid hydrolase gene, and this DNA fragment was amplified by the PCR method and utilized as the probe by which the full-length N-carbamyl-L-amino acid hydrolase gene of the present invention could be successfully isolated and obtained.

That is, as shown in FIG. 1, the hydantoinase gene and the N-carbamyl-L-amino acid hydrolase gene of the present invention are considered to be downstream from the hydantoin racemase gene, to form an operon together with the hydantoin racemase gene. In FIG. 1, (1) is an EcoRI/PstI fragment, (2) is a KpnI/SacI fragment, and (3) is a fragment cleaved with BglII.

The operation in the PCR method used in isolation of the genes is described by White, T. J. et al., in Trends Genet. 5, 185 (1989), etc. The method of preparing chromosomal DNA and the method of isolating a desired DNA molecule from a gene library by use of a probe DNA molecule are described in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989), etc.

The method of determining the nucleotide sequence of the isolated DNA encoding hydantoinase or N-carbamyl-L-amino acid hydrolase is described in A Practical Guide to Molecular Cloning, John Wiley & Sons, Inc. (1985), etc. Alternatively, the nucleotide sequence can be determined by use of a DNA sequencer manufactured by Applied Biosystems.

In the accompanying sequence listing of the present invention, the DNA encoding hydantoinase, specified by the method described above, is set forth in SEQ ID NO:1, and the DNA encoding N-carbamyl-L-amino acid hydrolase is set forth in SEQ ID NO:3. Further, the DNA encoding for a group of structural genes containing the hydantoin racemase gene, the hydantoinase gene and the N-carbamyl-L-amino acid hydrolase gene is set forth in SEQ ID NO:5.

These DNAs are those isolated from the chromosomal DNA in Microbacterium liquefaciens AJ3912 and encoding for the proteins involved in production of L-amino acids.

The amino acid sequence of a protein having a hydantoinase activity, encoded by the nucleotide sequence in SEQ ID NO:1 in the Sequence Listing, is set forth in SEQ ID NO: 2 in the Sequence Listing, and the amino acid sequence of a protein having an N-carbamyl-L-amino acid hydrolase activity, encoded by the nucleotide sequence in SEQ ID NO:3 in the Sequence Listing, is set forth in SEQ ID NO:4 in the Sequence Listing. In addition, the amino acid sequence of a protein having a hydantoin racemase activity (hydantoin racemase shown in Japanese Patent Application No. 2000-278571), encoded by the hydantoin racemase gene contained in the structural gene group set forth in SEQ ID NO:5, is set forth in SEQ ID NO:6 in the Sequence Listing.

The protein having a hydantoinase activity set forth in SEQ ID NO: 2 in the Sequence Listing and the protein having an N-carbamyl-L-amino acid hydrolase activity in SEQ ID NO: 4 in the Sequence Listing catalyze the reaction of forming an optically active amino acid represented by L-tyrosine from 5-substituted hydantoin represented by 5-(4-hydroxybenzyl) hydantoin, as shown in the following reaction scheme (III):

The DNA encoding hydantoinase and the DNA encoding N-carbamyl-L-amino acid hydrolase according to the present invention are described in more detail.

(1) DNA Encoding Hydantoinase

The hydantoinase gene of the present invention having the nucleotide sequence of SEQ ID NO: 1 in the Sequence Listing was isolated from the chromosomal DNA in Micobacterium liquefaciens AJ3912 as described above, and has 79% homology (85% homology in amino acid sequence) with a known hydantoinase gene derived from a microorganism of the genus Arthrobacter (J. Biotechnol. 80, 217 (2000)), and has 44% homology (17% homology in amino acid sequence) with a known hydantoinase gene derived from a microorganism of the genus Pseudomonas (J. Biotechnol. 174, 962 (1992)).

The protein encoded by the DNA shown in SEQ ID NO:1 in the Sequence Listing is characterized by having a hydantoinase activity toward 5-(4-hydroxybenzyl) hydantoin. Accordingly, this protein can be utilized preferably in production of optically active amino acids represented by L-tyrosine.

The DNA encoding hydantoinase according to the present invention is not limited to the DNA shown in SEQ ID NO:1 in the Sequence Listing. That is, the DNA must have a difference in the nucleotide sequence thereof among species and strains belonging to the genera Microbacterium and Flavobacterium.

As a matter of course, the DNA of the present invention encompasses not only the isolated DNA encoding hydantoinase, but also any DNAs encoding for hydantoinase obtained by artificially mutating the isolated DNA encoding hydantoinase. As a method used frequently for artificial mutation, there is the site-specific mutagenesis method described in Method. in Enzymol., 154 (1987).

The DNA of the present invention also encompasses a DNA encoding for a protein having a hydantoinase activity and having a nucleotide sequence hybridizing under stringent conditions with a DNA consisting of a nucleotide sequence complementary to the nucleotide sequence set forth in SEQ ID NO:1 in the Sequence Listing. As used herein, the “stringent conditions” refer to those conditions under which a specific hybrid is formed whereas an unspecific hybrid is not formed. These conditions are hardly expressed explicitly numerically, but by way of example, mention is made of those conditions under which DNA molecules having higher homology e.g. preferably 80% or more, more preferably 90% or more homology, hybridize with each other while DNA molecules having lower homology do not hybridize with each other, or those conditions under which hybridization occurs under usual washing conditions in Southern hybridization, that is, at a salt concentration corresponding to 1×SSC and 0.1% SDS at 60° C., preferably 0.1×SSC and 0.1% SDS at 60° C. The “hydantoinase activity” refers to the activity of hydrolyzing 5-substituted hydantoin compounds to form N-carbamyl amino acids. However, the nucleotide sequence hybridizing under stringent conditions with DNA consisting of a nucleotide sequence complementary to the nucleotide sequence shown in SEQ ID NO:1 in the Sequence Listing has desirably about at least half of the enzyme activity of a protein having the amino acid sequence shown in SEQ ID NO:2 in the Sequence Listing.

The DNA of the present invention encompasses a DNA encoding for the substantially the same protein as hydantoinase encoded by the DNA shown in SEQ ID NO:1 in the Sequence Listing, that is,

(a) DNA encoding for the amino acid sequence set forth in SEQ ID NO:2 in the Sequence Listing, and

(b) DNA encoding for a protein having a hydantoinase activity, which has an amino acid sequence wherein in the amino acid sequence set forth in SEQ ID NO:2 in the Sequence Listing, one or several amino acid residues are replaced, deleted, inserted, added or inverted.

To deduce the encoding DNA on the basis of the amino acid sequence in (a) or (b) above, DNA universal codons of the nucleotide sequence may be adopted.

The term “several” means a number which results in no substantial deterioration of the steric structure or enzymatic activity of the amino acid residues, and which is typically 2 to 50, preferably 2 to 30, more preferably 2 to 10. Further, the “hydantoinase activity” means the activity of hydrolyzing 5-substituted hydantoinase compounds to form N-carbamylamino acids. However, the protein wherein in the amino acid sequence set forth in SEQ ID NO:2 in the Sequence Listing, one or several amino acid residues are replaced, deleted, inserted, added or inverted has desirably about at least half of the enzyme activity of a protein having the amino acid sequence set forth in SEQ ID NO:2 in the Sequence Listing.

(2) DNA Encoding N-Carbamyl-L-Amino Acid Hydrolase

The DNA encoding N-carbamyl-L-amino acid hydrolase according to the present invention is explained. The N-carbamyl-L-amino acid hydrolase gene of the present invention having the nucleotide sequence set forth in SEQ ID NO:3 in the Sequence Listing was isolated from the chromosomal DNA in Microbacterium liquefaciens AJ3912, and has 74.2% homology (81% homology in amino acid sequence) with a known N-carbamyl-L-amino acid hydrolase gene derived from a microorganism of the genus Arthrobacter (J. Biotechnol. 68, 101 (1999)). Further, this DNA has 47% homology (39% homology in amino acid sequence) with a known N-carbamyl-L-amino acid hydrolase gene derived from a microorganism of the genus Pseudomonas (J. Biotechnol. 174, 962 (1992)).

The DNA encoding N-carbamyl-L-amino acid hydrolase according to the present invention is not limited to the DNA shown in SEQ ID NO:3 in the Sequence Listing. That is, the DNA must have a difference in the nucleotide sequence thereof among species and strains belonging to the genera Microbacterium and Flavobacterium.

A DNA encoding N-carbamyl-L-amino acid hydrolase, even if obtained by artificially mutating the isolated DNA encoding N-carbamyl-L-amino acid hydrolase, is the DNA of the present invention. As a method used frequently for artificial mutation, there is the site-specific mutagenesis method described in Method. in Enzymol., 154 (1987).

The DNA of the present invention also encompasses a DNA encoding for a protein having an N-carbamyl-L-amino acid hydrolase activity and having a nucleotide sequence hybridizing under stringent conditions with a DNA consisting of a nucleotide sequence complementary to the nucleotide sequence set forth in SEQ ID NO:3 in the Sequence Listing. As used herein, the “stringent conditions” refer to those conditions under which a specific hybrid is formed whereas an unspecific hybrid is not formed. These conditions are hardly expressed explicitly numerically, but by way of example, mention is made of those conditions under which DNA molecules having higher homology e.g. preferably 80% or more, more preferably 90% or more homology, hybridize with each other while DNA molecules having lower homology do not hybridize with each other, or those conditions under which hybridization occurs under usual washing conditions in Southern hybridization, that is, at a salt concentration corresponding to 1×SSC and 0.1% SDS at 60° C., preferably 0.1×SSC and 0.1% SDS at 60° C. The “N-carbamyl-L-amino acid hydrolase activity” refers to the activity of hydrolyzing N-carbamylamino acids to form L-amino acids. However, the nucleotide sequence hybridizing under stringent conditions with DNA consisting of a nucleotide sequence complementary to the nucleotide sequence shown in SEQ ID NO:3 in the Sequence Listing has desirably about at least half of the enzyme activity of a protein having the amino acid sequence shown in SEQ ID NO:4 in the Sequence Listing.

The DNA of the present invention encompasses a DNA encoding for the substantially the same protein as N-carbamyl-L-amino acid hydrolase encoded by the DNA, that is,

(a) DNA encoding for the amino acid sequence set forth in SEQ ID NO:4 in the Sequence Listing, and

(b) DNA encoding for a protein having an N-carbamyl-L-amino acid hydrolase activity, which has an amino acid sequence wherein in the amino acid sequence set forth in SEQ ID NO:4 in the Sequence Listing, one or several amino acid residues are replaced, deleted, inserted, added or inverted.

To deduce the encoding DNA on the basis of the amino acid sequence in (a) or (b) above, DNA universal codons of the nucleotide sequence may be adopted.

The term “several” means a number which results in no substantial deterioration of the steric structure or enzymatic activity of the amino acid residues, and which is typically 2 to 50, preferably 2 to 30, more preferably 2 to 10. Further, the “N-carbamyl-L-amino acid hydrolase activity” means the activity of hydrolyzing N-carbamyl-L-amino acids to form L-amino acids. However, the protein wherein in the amino acid sequence set forth in SEQ ID NO: 4 in the Sequence Listing, one or several amino acid residues are replaced, deleted, inserted, added or inverted has desirably about at least half of the enzyme activity of a protein having the amino acid sequence set forth in SEQ ID NO:4 in the Sequence Listing.

[II] Method of Producing Hydantoinase and N-Carbamyl-L-Amino Acid Hydrolase

The method of producing hydantoinase and N-carbamyl-L-amino acid hydrolase by recombinant DNA technology is explained. A large number of examples where useful proteins such as enzymes, physiologically active substances etc. are produced by utilizing recombinant DNA technology are known, and by use of recombinant DNA technology, useful proteins present in a very small amount in nature can be produced in a large amount.

FIG. 2 is a flowchart of the process of producing hydantoinase and N-carbamyl-L-amino acid hydrolase according to the present invention.

The hydantoinase gene of the present invention and/or the DNA encoding N-carbamyl-L-amino acid hydrolase is prepared (step S1).

The prepared DNA is ligated to a vector DNA to prepare a recombinant DNA (step S2), and cells are transformed with the recombinant DNA, to prepare a transformant (step S3). Subsequently, the transformant is cultured in a medium to form and accumulate hydantoinase and/or N-carbamyl-L-amino acid hydrolase in the medium and/or cells (step S4).

Thereafter, the enzyme is recovered and purified in step S5, whereby the hydantoinase and/or N-carbamyl-L-amino acid hydrolase is produced in a large amount.

The enzyme produced in step S5 or the medium containing the enzyme accumulated therein in step S4 is used in synthesis of amino acid, whereby the desired optically active amino acid can be produced in a large amount (step S6).

The DNA ligated to the vector DNA may be any DNA capable of expressing the hydantoinase and/or N-carbamyl-L-amino acid hydrolase of the present invention.

As the hydantoinase gene ligated to the vector DNA, it is possible to use the above-described DNA, for example:

(a) DNA having the nucleotide sequence set forth in SEQ ID NO:1 in the Sequence Listing,

(b) DNA having a nucleotide sequence hybridizing under stringent conditions with DNA consisting of a nucleotide sequence complementary to the nucleotide sequence set forth in SEQ ID NO:1 in the Sequence Listing,

(c) DNA encoding for the amino acid sequence set forth in SEQ ID NO:2 in the Sequence Listing, and

(d) DNA encoding for an amino acid sequence wherein in the amino acid sequence set forth in SEQ ID NO:2 in the Sequence Listing, one or several amino acid residues are replaced, deleted, inserted, added or inverted.

As the N-carbamyl-L-amino acid hydrolase gene ligated to the vector DNA, it is possible to use e.g. the following DNAs:

(a) DNA having the nucleotide sequence set forth in SEQ ID NO: 3 in the Sequence Listing,

(b) DNA having a nucleotide sequence hybridizing under stringent conditions with DNA consisting of a nucleotide sequence complementary to the nucleotide sequence set forth in SEQ ID NO:3 in the Sequence Listing,

(c) DNA encoding for the amino acid sequence set forth in SEQ ID NO:4 in the Sequence Listing, and

(d) DNA encoding for an amino acid sequence wherein in the amino acid sequence set forth in SEQ ID NO: 4 in the Sequence Listing, one or several amino acid residues are replaced, deleted, inserted, added or inverted.

In addition to these DNAs, use can be made of DNA comprising the hydantoinase gene ligated to the N-carbamyl-L-amino acid hydrolase gene or DNA having the nucleotide sequence shown in SEQ ID NO:5 in the Sequence Listing. In the case of the former, the hydantoinase of the present invention and the N-carbamyl-L-amino acid hydrolase of the present invention will be simultaneously expressed, while in the case of the latter, not only the hydantoinase and N-carbamyl-L-amino acid hydrolase of the present invention but also hydantoin racemase will be expressed.

When the protein is to be produced in a large mount by recombinant DNA technology, host cells to be transformed can make use of microbial cells, Actinomyces cells, yeast cells, fungal cells, plant cells, animal cells etc. Because there are generally a large number of findings on production of proteins in a large amount by use of colon bacteria, it is preferable to use Escherichia coli. Hereinafter, the method of producing hydantoinase and/or N-carbamyl-L-amino acid hydrolase by use of transformed colon bacteria is explained.

As the promoter expressing the DNA encoding hydantoinase and/or N-carbamyl-L-amino acid hydrolase, a promoter ordinarily used in production of a protein in colon bacteria can be used, and mention can be made of strong promoters such as, for example, T7 promoter, trp promoter, lac promoter, tac promoter, PL promoter etc.

To increase the amount of the protein produced, a terminator that is a transcription termination sequence is preferably ligated to a downstream region of the protein gene. The terminator includes T7 terminator, fd phage terminator, T4 terminator, a terminator for tetracycline resistance gene, a terminator for colon bacteria trp A gene, etc.

The vector for introducing the gene encoding for hydantoinase and/or N-carbamyl-L-amino acid hydrolase into host cells is preferably the so-called multicopy vector, and includes plasmids having an origin of replication derived from Col E1, for example, pUC series plasmids, pBR322 series plasmids or derivatives thereof. The “derivatives” are those obtained by modifying plasmids by replacement, deletion, insertion, addition or inversion of some nucleotides. The modification referred to here includes modification by natural mutation or by mutation treatment with a mutagen or UV irradiation.

To select the transformant, the vector preferably has a marker such as ampicillin resistance gene etc., and as such plasmids, expression vectors having a strong promoter are commercially available; for example, pUC series (manufactured by Takara Shuzo Co., Ltd.), pPROK series (manufactured by Clontech), pKK233-2 (manufactured by Clontech) etc.

The DNA fragment having a promoter, the gene encoding for hydantoinase and/or N-carbamyl-L-amino acid hydrolase, and a terminator ligated in this order can be ligated to the vector DNA to give a recombinant DNA.

The recombinant DNA is used to transform host cell, and by culturing the cells, the hydantoinase and/or N-carbamyl-L-amino acid hydrolase is expressed and produced. As the method of transformation and the method of selecting the transformant, those described in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989), etc. can be used.

The production medium used may be a medium such as M9-casamino acid medium, LB medium etc. which are usually used for culturing colon bacteria. Further, the culture conditions and production-inducing conditions are selected suitably depending on the marker and promoter in the vector used, the type of the host microorganism, etc. To increase the amount of the enzyme produced, addition of isopropyl-1-thio-β-D-galactopyranoside (IPTG) to the medium or enzyme-inducing treatments such as an increase in temperature are also preferable.

After the cultured microorganism is collected by centrifugation etc., the microorganism is disrupted or lyzed, and hydantoinase and/or N-carbamyl-L-amino acid hydrolase can be recovered and used as a crude enzyme. Disruption of the microorganism can make use of methods such as disruption by sonication, disruption by a French press, disruption by glass beads etc.; or when the microorganism is to be lyzed, a method of treatment with egg white lysozyme or a peptidase or a method of suitable combination thereof is used. As necessary, these enzymes can be used in a pure form after purification by conventional techniques such as precipitation, filtration and column chromatography. In this case, a method of purification with an antibody against these enzymes can also be used.

The hydantoinase of the present invention obtained by the method of using the recombinant described above is a protein having a hydantoinase activity, which has the following amino acid sequence (a) or (b):

(a) the amino acid sequence set forth in SEQ ID NO:2 in the Sequence Listing, and

(b) an amino acid sequence wherein in the amino acid sequence set forth in SEQ ID NO:2 in the Sequence Listing, one or several amino acid residues are replaced, deleted, inserted, added or inverted.

The N-carbamyl-L-amino acid hydrolase of the present invention obtained by the method of using the recombinant described above is a protein having an N-carbamyl-L-amino acid hydrolase activity, which has the following amino acid sequence (a) or (b):

(a) the amino acid sequence set forth in SEQ ID NO:4 in the Sequence Listing, and

(b) an amino acid sequence wherein in the amino acid sequence set forth in SEQ ID NO:4 in the Sequence Listing, one or several amino acid residues are replaced, deleted, inserted, added or inverted.

The “one or several amino acid residues”, “hydantoinase activity” and “N-carbamyl-L-amino acid hydrolase activity” have the same meanings as defined in the item [I] DNA encoding hydantoinase and N-carbamyl-L-amino acid hydrolase.

[III] Method of Producing an Optically Active Amino Acid

The method of producing an optically active amino acid by use of the hydantoinase and/or N-carbamyl-L-amino acid hydrolase according to the present invention is explained.

The method of producing an optically active amino acid according to the present invention comprises use of the enzyme of the present invention as hydantoinase and/or N-carbamyl-L-amino acid hydrolase, and there can be the following 3 combinations of hydantoinase and N-carbamyl-L-amino acid hydrolase:

(i) hydantoinase of the present invention+N-carbamylamino acid hydrolase,

(ii) hydantoinase+N-carbamyl-L-amino acid hydrolase of the present invention, and

(iii)) hydantoinase of the present invention+N-carbamyl-L-amino acid hydrolase of the present invention.

In case (i), the hydantoinase of the present invention includes a protein having a hydantoinase activity, which has the following amino acid sequence (a) or (b):

(a) the amino acid sequence set forth in SEQ ID NO:2 in the Sequence Listing, and

(b) an amino acid sequence wherein in the amino acid sequence set forth in SEQ ID NO:2 in the Sequence Listing, one or several amino acid residues are replaced, deleted, inserted, added or inverted.

The hydantoinase obtained by culturing cells transformed with a recombinant DNA obtained by ligating the DNA encoding for such hydantoinase to a vector can also be used. When the hydantoinase is produced by the transformed cells, a substrate may be added directly to a culture liquid thereof during culturing, and either the microorganism separated from the culture liquid or the washed microorganism can be used. Further, a treated microbial material prepared by disrupting or lyzing the microorganism may be used as it is, or the hydantoinase may be recovered from the treated microbial material and used as a crude enzyme solution, and the enzyme may be further purified before use. That is, the enzyme and materials containing the enzyme as fractions having a hydantoinase activity can be used. The “materials containing the enzyme” may be any materials containing the enzyme, and include e.g. a culture, a cultured microorganism, a washed microorganism, a treated microbial material obtained by disrupting or lyzing the microorganism, a crude enzyme solution, a purified enzyme, etc.

As the substrate for the hydantoinase of the present invention, any 5-substituted hydantoin compounds which can be hydrolyzed with the substrate specificity of the enzyme, and both D- and L-5-substituted hydantoin compounds can be used. For example, mention is made of 5-substituted hydantoin compounds corresponding to naturally occurring amino acids, typically DL-5-benzyl hydantoin, DL-5-(4-hydroxybenzyl) hydantoin, DL-5-indolyl methyl hydantoin, DL-5-(3,4-dihydroxybenzyl) hydantoin, DL-5-methyl thioethyl hydantoin, DL-5-isobutyl hydantoin, DL-5-carbamyl ethyl hydantoin and DL-5-carbamyl methyl hydantoin, etc. and 5-substituted hydantoin compounds corresponding to non-naturally occurring amino acids, typically DL-5-benzyl oxymethyl hydantoin, DL-5-(3,4-methylene dioxybenzyl) hydantoin, DL-5-(3,4-dimethoxybenzyl) hydantoin, DL-5-methoxymethyl hydantoin, and DL-5-(4-methyl-4-nitropentyl) hydantoin, etc. as well as 5-substituted hydantoin compounds corresponding to derivatives of the above.

As the N-carbamylamino acid hydrolase used in combination with the hydantoinase of the present invention, the known enzyme catalyzing the reaction of forming an amino acid by acting on N-carbamylamino acid to hydrolyze the substance, or materials containing the enzyme, can be used without particular limitation. The “materials containing the enzyme” may be any materials containing the enzyme, and include e.g. a culture, a cultured microorganism, a treated microbial material obtained by disrupting or lyzing the microorganism, a crude enzyme solution, a purified enzyme, etc. However, the hydantoinase of the present invention does not have optical selectivity, so when optically active amino acids are to be produced from DL-5-substituted hydantoin compounds as the starting material, optically selective N-carbamylamino acid hydrolase should be used. The presence of N-carbamyl-D-amino acid hydrolase selectively hydrolyzing a D-configuration of N-carbamylamino acid in for example Pseudomonas sp. AJ11220 (Japanese Patent Application Publication No. 56-003034) is known. As a result of re-identification, Pseudomonas sp. AJ11220 is revealed to belong Agrobacterium sp. Agrobacterium sp. AJ11220 is a microorganism deposited on Dec. 20, 1977 as FERM-P4347 with the National Institute of Bioscience and Human-Technology, the Agency of Industrial Science of Technology, the Ministry of International Trade and Industry, JP and transferred on Jun. 27, 2001 as FERM BP-7645 under the Budapest Treaty to International Patent Organism Depositary (IPOD), National Institute of Advanced Industrial Science and Technology (AIST) (ChuoNo. 6, Higashi 1-1-1, Tsukuba City, Ibaraki Pref., JP, 305-8566). Further, the presence of N-carbamyl-L-amino acid hydrolase selectively hydrolyzing the L-configuration of N-carbamylamino acid in e.g. Bacillus sp. AJ12299 (Japanese Patent Application Laid-Open No. 63-024894) besides Microbacterium liquefaciens AJ3912 shown in the present invention is known. Bacillus sp. AJ12299 is a microorganism deposited on Jul. 5, 1986 under FERM-P8837 with the National Institute of Bioscience and Human-Technology, the Agency of Industrial Science of Technology, the Ministry of International Trade and Industry, JP and transferred on Jun. 27, 2001 as FERM BP-7646 under the Budapest Treaty to International Patent Organism Depositary (IPOD), National Institute of Advanced Industrial Science and Technology (AIST) (Chuo No. 6, Higashi 1-1-1, Tsukuba City, Ibaraki Pref., JP, 305-8566).

The case (ii) will now be explained. The N-carbamyl-L-amino acid hydrolase of the present invention includes a protein having an N-carbamyl-L-amino acid hydrolase activity, which has the following amino acid sequence (a) or (b):

(a) the amino acid sequence set forth in SEQ ID NO:4 in the Sequence Listing, and

(b) an amino acid sequence wherein in the amino acid sequence set forth in SEQ ID NO:4 in the Sequence Listing, one or several amino acid residues are replaced, deleted, inserted, added or inverted.

The N-carbamyl-L-amino acid hydrolase obtained by culturing cells transformed with a recombinant DNA obtained by ligating the DNA encoding for such N-carbamyl-L-amino acid hydrolase to a vector can also be used. When the N-carbamyl-L-amino acid hydrolase is produced by the transformed cells, a substrate may be added directly to a culture liquid thereof during culturing, and either the microorganism separated from the culture or the washed microorganism can be used. Further, a treated microbial material prepared by disrupting or lyzing the microorganism may be used as it is, or the N-carbamyl-L-amino acid hydrolase may be recovered from the treated microbial material and used as a crude enzyme solution, and the enzyme may be further purified before use. That is, the enzyme and materials containing the enzyme as fractions having an N-carbamyl-L-amino acid hydrolase activity can be used. The “materials containing the enzyme” may be any materials containing the enzyme, and include e.g. a culture, a cultured microorganism, a washed microorganism, a treated microbial material obtained by disrupting or lyzing the microorganism, a crude enzyme solution, a purified enzyme, etc.

As the substrate for the N-carbamyl-L-amino acid hydrolase of the present invention, any N-carbamyl-L-amino acids which can be hydrolyzed with the substrate specificity of the enzyme can be used. That is, not only N-carbamyl-L-amino acids obtained from the 5-substituted hydantoin compounds described above, but also N-carbamyl-L-serine, N-carbamyl-L-glycine, N-carbamyl-L-isoleucine, N-carbamyl-L-valine, N-carbamyl-L-alanine and N-carbamyl-β-alanine, etc. can be used as the substrate.

As the hydantoinase used in combination with the N-carbamyl-L-amino acid hydrolase of the present invention, the known enzyme catalyzing the reaction of forming N-carbamylamino acid by acting on a 5-substituted hydantoin compound to hydrolyze the substance, or materials containing the enzyme, can be used without particular limitation. The “materials containing the enzyme” may be any materials containing the enzyme, and include e.g. a culture, a cultured microorganism, a treated microbial material obtained by disrupting or lyzing the microorganism, a crude enzyme solution, a purified enzyme, etc. However, the N-carbamyl-L-amino acid hydrolase of the present invention is specific to L-configuration, so optical specificity-free hydantoinase or hydantoinase acting specifically on L-configuration should be used. The presence of the optical specificity-free hydantoinase in e.g. Arthrobacter aurescens besides Microbacterium liquefaciens AJ3912 shown in the present invention is known (J. Biotechnol. 61, 1 (1998)). Further, the presence of the hydantoinase acting specifically on the L configuration of hydantoin compound in e.g. Bacillus sp. AJ12299 (Japanese Patent Application Laid-Open No. 63-024894) is known. Bacillus sp. AJ12299 is a microorganism deposited on Jul. 5, 1986 under FERM-P8837 with the National Institute of Bioscience and Human-Technology, the Agency of Industrial Science of Technology, the Ministry of International Trade and Industry, JP and transferred on Jun. 27, 2001 as FERM BP-7646 under the Budapest Treaty to International Patent Organism Depositary (IPOD), National Institute of Advanced Industrial Science and Technology (AIST) (ChuoNo. 6, Higashi 1-1-1, Tsukuba City, Ibaraki Pref., JP, 305-8566).

The case (iii) will now be explained. In case (iii), the hydantoinase of the present invention described in (i) is used in combination with the N-carbamyl-L-amino acid hydrolase of the present invention explained in (ii). Among the combinations in (i) to (iii), the most preferable combination is (iii).

In the reaction process, a mixture of the hydantoinase and N-carbamyl-L-amino acid hydrolase may be allowed to react on 5-substituted hydantoin compounds, or the hydantoinase and N-carbamyl-L-amino acid hydrolase may be successively allowed to react on 5-substituted hydantoin compounds. From the viewpoint of simplification of the reaction process, the former method is preferable.

When the hydrolysis activity of the hydantoinase is free of optical selectivity and the N-carbamylamino acid hydrolase has optical activity when DL 5-substituted hydantoin compounds are converted into optically active amino acids, the formed amino acids will be either D- or L-optically active amino acids while the unreacted enantiomer N-carbamylamino acids will remain in the reaction solution. That is, when L-amino acids are formed by selectively decomposing N-carbamyl-L-amino acids by the N-carbamylamino acid hydrolase, N-carbamyl-D-amino acids will remain; on the other hand, when D-amino acids are formed, N-carbamyl-L-amino acids will remain.

Even in this case, however, the hydantoinase slightly catalyze the reverse reaction i.e. dehydration and condensation of the remaining unreacted enantiomer N-carbamylamino acids, to form 5-substituted hydantoin compounds again.

Accordingly, the optically active amino acids can be produced in a molar ratio of 50% or more from DL 5-substituted hydantoin compounds by combination with spontaneous racemization or chemical racemization of 5-substituted hydantoin compounds or racemization reaction by hydantoin racemase.

In other words, it is preferable to further use hydantoin racemase in addition to the hydantoinase and N-carbamyl-L-amino acid hydrolase. As the hydantoin racemase, hydantoin racemase derived from Aureobacterium liquefaciens AJ3912 (FERM-P 3133) described in Japanese Patent Application No. 2000-278571 can be preferably used. In this case, a hybrid protein consisting of hydantoin racemase, hydantoinase and N-carbamyl-L-amino acid hydrolase obtained by culturing cells transformed with a recombinant DNA obtained by ligating, to a vector, a structural gene group shown in SEQ ID NO:5 encoding for the proteins involved in production of L-amino acid can also be used. When the hybrid protein is used, the hydantoin racemase contained in the hybrid protein catalyzes racemization of 5-substituted hydantoin compounds, and thus L-amino acids can be obtained theoretically 100% yield from DL 5-substituted hydantoin compounds as shown in the following reaction scheme (IV). When the hybrid protein is used, the hydantoinase also catalyzes a reverse reaction of a reaction that produces an N-carbamylamino acid by splitting or causing cleavage of a hydantoin ring. In other words, the hydantoinase catalyzes the reverse reaction that produces 5-substituted hydantoin from N-carbamylamino acid. Therefore, L-amino acid may be produced also from N-carbamyl-D-amino acid.

The hybrid protein can also be used to produce N-carbamylamino acids. For example, N-carbamylamino acids can be produced by adding e.g. an inhibitor of the N-carbamyl-L-amino acid hydrolase to the hybrid protein, to terminate the hydrolysis reaction at the stage of N-carbamylamino acids.

In production of optically active amino acids, the remaining N-carbamylamino acids may be separated and recovered from optically active amino acid, whereby the N-carbamylamino acids can be produced. Further, amino acids can then be produced by allowing the N-carbamylamino acid hydrolase or materials containing the enzyme to act on the N-carbamylamino acids; or by chemical hydrolysis treatment with nitrite etc., the amino acids can also be produced in higher yield maintaining optical activity.

The presence of N-carbamyl-D-amino acid hydrolase selectively hydrolyzing the D-configuration of N-carbamylamino acid in e.g. Pseudomonas sp. AJ11220 is known (Japanese Patent Application Publication No. 56-003034). As a result of re-identification, Pseudomonas sp. AJ11220 is revealed to belong Agrobacterium sp. Agrobacterium sp. AJ11220 is a microorganism deposited on Dec. 20, 1977 as FERM-P4347 with the National Institute of Bioscience and Human-Technology, the Agency of Industrial Science of Technology, the Ministry of International Trade and Industry, JP and transferred on Jun. 27, 2001 as FERM BP-7645 under the Budapest Treaty to International Patent Organism Depositary (IPOD), National Institute of Advanced Industrial Science and Technology (AIST) (ChuoNo. 6, Higashi 1-1-1, Tsukuba City, IbarakiPref., JP, 305-8566). Further, the presence of N-carbamyl-L-amino acid hydrolase selectively hydrolyzing the L-configuration of N-carbamylamino acid in e.g. Bacillus sp. AJ12299 (Japanese Patent Application Laid-Open No. 63-024894) besides Microbacterium liquefaciens AJ3912 shown in the present invention is known. Bacillus sp. AJ12299 is a microorganism deposited on Jul. 5, 1986 under FERM-P8837 with the National Institute of Bioscience and Human-Technology, the Agency of Industrial Science of Technology, the Ministry of International Trade and Industry, JP and transferred on Jun. 27, 2001 as FERM BP-7646 under the Budapest Treaty to International Patent Organism Depositary (IPOD), National Institute of Advanced Industrial Science and Technology (AIST) (Chuo No. 6, Higashi 1-1-1, Tsukuba City, Ibaraki Pref., JP, 305-8566).

When a culture liquid of cells transformed with the recombinant DNA obtained by linking the DNA encoding hydantoinase and/or N-carbamyl-L-amino acid hydrolase to a vector DNA, or a separated microorganism, a washed microorganism, a treated microbial material, or a crude enzyme solution or a purified enzyme obtained from the treated microbial material is used for progress of the amino acid-forming reaction, a reaction solution containing 5-substituted hydantoin compounds or N-carbamylamino acid, and the culture liquid, the separated microorganism, the washed microorganism, the treated microbial material, the crude enzyme solution, or the purified enzyme is adjusted to a suitable temperature of 25 to 40° C. and left or stirred for 8 hours to 5 days while the pH is kept at 5 to 9.

When the cells transformed with the recombinant DNA obtained by linking the DNA encoding hydantoinase and/or N-carbamyl-L-amino acid hydrolase to a vector DNA are cultured in a water-soluble medium to proceed the amino acid-forming reaction, use is made of a water-soluble medium containing 5-substituted hydantoin compounds or N-carbamylamino acid, nutrients such as a carbon source, a nitrogen source, and inorganic ions necessary for growth of the transformed cells. Further, desirable results are often obtained by adding a very small amount of organic nutrients such as vitamins, amino acids etc. The 5-substituted hydantoin compounds may be added in divided portions. Culturing is conducted preferably for 8 hours to 5 days under aerobic conditions while maintaining a suitable range of pH 5 to 9 and a temperature of 25 to 40° C.

The formed amino acids can be separated and purified by techniques known in the art. For example, there is a method of adsorbing basic amino acids by contacting with an ion-exchange resin and then eluting them, followed by crystallization thereof or discoloration and filtration thereof through activated carbon and subsequent crystallization.

EXAMPLES

Hereinafter, the present invention is explained in more detail by reference to Examples 1 to 5. The present invention is not limited to the description of the Examples.

Example 1 Isolation of a Hydantoinase Gene and an N-Carbamyl-L-Amino Acid Hydrolase Gene

As described above, the present inventors estimated that in isolation and purification of a hydantoin racemase gene from cultured Microbacterium liquefaciens AJ3912, a simultaneously obtained nucleotide sequence downstream from the hydantoin racemase gene is apart of a hydantoinase gene because of homology thereof with a known hydantoinase gene, and further estimated that an N-carbamyl-L-amino acid hydrolase gene can be present downstream therefrom, and thus the inventors utilized such DNA fragment as the probe by which the full-length hydantoinase gene and the full-length N-carbamyl-L-amino acid hydrolase gene were obtained from a gene library of the above strain. For configuration of the gene library, E. coli JM109 was used as the host, and pUC18 or pUC19 was used as the vector.

1. Acquisition of the Microorganism

Microbacterium liquefaciens AJ3912 was refreshed by culturing it at 30° C. for 24 hours in CM2G agar medium (0.5 g/dl glucose, 1.0 g/dl yeast extract, 1.0 g/dl peptone, 0.5 g/dl NaCl, 2 g/dl agar, pH 7.0). The microorganism was inoculated via one loop of platinum into a 500-ml Sakaguchi flask containing 50 ml CM2G liquid medium, and then cultured under shaking at 30° C. for 16 hours under aerobic conditions.

2. Acquisition of the Chromosomal DNA from the Microorganism

50 ml of the culture liquid was centrifuged (12,000×g, 4° C., 15 minutes), whereby the microorganism was collected. This microorganism was suspended in 10 ml of 50:20 TE (50 mM Tris-HCl (pH 8.0), 20 mM EDTA), washed and centrifuged, whereby the microorganism was recovered, and then this microorganism was suspended again in 10 ml of 50:20 TE. 0.5 ml of 20 mg/ml lysozyme solution and 1 ml of 10% SDS solution were added to the above suspension, followed by incubation at 55° C. for 20 minutes. After incubation, a 1-fold volume of 10:1 TE-saturated phenol was added thereto to remove proteins. A 1-fold volume of 2-propanol was added to the separated aqueous layer, to precipitate and recover DNA. After the precipitated DNA was dissolved in 0.5 ml of 50:20 TE, 5 μl of 10 mg/ml RNase and 5 μl of 10 mg/ml Proteinase K were added thereto and the mixture was reacted at 55° C. for 2 hours. After reaction, a 1-fold volume of 10:1 TE-saturated phenol was added thereto to remove proteins. Further, a 1-fold volume of 24:1 chloroform/isoamyl alcohol was added to the separated aqueous layer and stirred, and the aqueous layer was recovered. This procedure was repeated further twice, and 3 M sodium acetate solution (pH 5.2) was added at a final concentration of 0.4 M to the resulting aqueous layer, followed by adding a 2-fold volume of ethanol thereto. The DNA occurring as precipitates was recovered, washed with 70% ethanol, dried and dissolved in 1 ml of 10:1 TE.

3. Isolation of the Hydantoinase Gene

By a method described in Japanese Patent Application No. 2001-278739, it was confirmed that in an about 2.9 kb EcoRI/PstI fragment ((1) in FIG. 1) obtained from the chromosomal DNA in Microbacterium liquefaciens AJ3912, there is an open reading frame (ORF) encoding for a protein containing an N-terminal amino acid sequence of hydantoin racemase, and that this gene is a gene encoding for hydantoin racemase having 48% homology with a known hydantoin racemase derived from a microorganism of the genus Pseudomonas (J. Bacteriol., 174, 962 (1992)). In this 2.9 kb fragment, a downstream region of about 600 nucleotides from the hydantoin racemase gene was examined for homology, and as a result, it was confirmed that a region of from the nucleotide at the 18-position (from the termination codon of the hydantoin racemase gene) to PstI site has homology with a known hydantoinase. Accordingly, apart of this sequence was used in an attempt at acquisition of the full-length hydantoinase gene. The contents of the patent applications supra are incorporated by reference into this specification.

4. Isolation of the Hydantoinase Gene from the Gene Library

Southern hybridization was carried out for acquisition of the full-length hydantoinase gene. By PCR where the chromosomal DNA from Microbacterium liquefaciens AJ3912 was used as the template while the oligonucleotides shown in Table 2 were used as primers, a fragment (about 500 bp in the above region of about 600 bp) was amplified and used as the probe. The amplified fragment was prepared at a concentration of about 50 nm/μl, and as the probe, 16 μl of this DNA solution was labeled with DIG by incubation at 37° C. for 24 hours according to a protocol of DIG High Prime (Boehringer Mannheim).

Table 2

Primers used for preparation of the probe for acquisition of the hydantoinase gene

Primer  No. Sequence 10 CTGCAGCGTCTGGATGAGCATCTCGTTCTCGG  SEQ ID NO: 7 16 ATCGATGCCGCAGGCAGGTTCGTGATGCC  SEQ ID NO: 8

1 μg chromosomal DNA was completely digested with a combination of various restriction enzymes, subjected to electrophoresis on 0.8% agarose gel, and blotted onto a nylon membrane (Boehringer Mannheim, Nylon membranes positively charged). Subsequently, Southern hybridization was conducted according to the conventional method. Hybridization was carried out using DIG Easy Hyb (Boehringer Mannheim), and after pre-hybridization at 50° C. for 30 minutes, the probe was added and hybridized at 50° C. for 18 hours. The sample was detected using a DIG Nucleotide Detection Kit (Boehringer Manheim).

As a result, a band was detected at a position of about 1.5 kb in a KpnI/SacI-cleaved product ((2) in FIG. 1). Accordingly, a fragment of about 1.5 kb was recovered from the cleaved product and ligated to pUC19, to prepare a library (450 strains) of E. coli JM109, followed by colony hybridization. The colonies were transferred onto a nylon membrane filter (Boehringer Mannheim, Nylon membranes for colony and plaque hybridization) and subjected to treatments such as alkali denaturation, neutralization and immobilization. Hybridization was conducted using DIG Easy Hyb, pre-hybridization was conducted at 42° C. for 30 minutes, and then the DIG-labeled probe described above was added thereto and hybridized at 42° C. for 18 hours. Five positive clones were selected by detecting with a DIG Nucleotide Detection Kit.

The plasmid carried on the selected clones was prepared according to a method described in Molecular Cloning, 2nd edition, Cold Spring Harbor Press (1989), and the nucleotide sequence of the inserted fragment was determined. As a result, an about 1.4-kb open reading frame (ORF) was present downstream from the hydantoin racemase gene, and estimated to be a hydantoinase gene. The nucleotide sequence of the full-length hydantoinase gene is shown in SEQ ID NO:1, and its corresponding amino acid sequence is shown in SEQ ID NO:2. The resultant hydantoinase gene had 17% homology in amino acid sequence with a known hydantoinase gene derived from a microorganism of the genus Pseudomonas (J. Bacterial. 174, 962 (1992)). From this about 1.5-kb fragment, an about 40-bp sequence downstream from the hydantoinase gene was obtained, and this sequence was confirmed to have homology with a known N-carbamyl-L-amino acid hydrolase gene. Accordingly, it was attempted to obtain the full-length N-carbamyl-L-amino acid hydrolase gene.

5. Isolation of the N-Carbamyl-L-Amino Acid Hydrolase Gene from the Gene Library

For acquisition of the N-carbamyl-L-amino acid hydrolase gene, Southern hybridization was carried out. By PCR where the chromosomal DNA from Microbacterium liquefaciens AJ3912 was used as the template while the oligonucleotides shown in Table 3 were used as primers, a fragment (a part of the hydantoinase gene; about 0.8 kb) was amplified and used as the probe. The amplified fragment was prepared at a concentration of about 50 ng/μl, and as the probe, 16 μl of this DNA solution was labeled with DIG by incubation at 37° C. for 24 hours according to a protocol of DIG High Prime.

Table 3

Primers used for preparation of the probe for acquisition of the N-carbamyl-L-amino acid hydrolase gene

Primer No. Sequence 18 ACGCCGAGAACGAGATGCTCATCCAGACGC SEQ ID NO: 9 45 GGTCACGAACTGCCCGAACCCCT SEQ ID NO: 10

Using this labeled probe, Southern hybridization was carried out in the method mentioned above, whereby a band was detected at a position of about 3.4 kb in a BglII-cleaved product ((3) in FIG. 1). From the cleaved product, a fragment of about 3.4 kb was recovered and ligated to pUC18 to prepare a library (150 strains) of E. coli JM109. Then, colony hybridization was carried out in the manner described above, to select one positive clone.

The plasmid carried on the selected clone was prepared, and the nucleotide sequence of the inserted fragment was determined, and as a result, an about 1.2-kb ORF was present downstream from the hydantoinase gene, and estimated to be an N-carbamyl-L-amino acid hydrolase gene. The nucleotide sequence of the full-length N-carbamyl-L-amino acid hydrolase gene is shown in SEQ ID NO: 3 in the Sequence Listing, and its corresponding amino acid sequence is shown in SEQ ID NO:4 in the Sequence Listing. The resultant N-carbamyl-L-amino acid hydrolase gene had 39% homology in amino acid sequence with a known N-carbamyl-L-amino acid hydrolase gene derived from the genus Pseudomonas (J. Bacterial. 174, 962 (1992)).

Example 2 Expression of the Hydantoinase Gene and N-Carbamyl-L-Amino Acid Hydrolase Gene in E. coli

1. Construction of an Expression Plasmid

To express the two genes in E. coli, plasmids pUCCH and pUCCH having the two genes ligated to a downstream region from a lac promoter in pUC18 were constructed in the following manner. First, each gene was amplified (the hydantoinase gene was amplified to nucleotide 29 downstream of the termination codon) by PCR where the chromosomal DNA in Microbacterium liquefaciens AJ3912 was used as the template while the oligonucleotides shown in Table 4 were used as primers. The amplified fragments were treated with EcoRI and BamHI, ligated to an EcoRI- and BamHI-cleaved fragment of pUC18, and introduced into E. coli JM109. From ampicillin resistance strains, a strain having the desired plasmids were selected, and the plasmids were designated expression plasmids pUCHH and pUCCH respectively.

TABLE 4 Primers used in amplification of the hydantoinase gene and N-carbamyl-L-amino acid hydrolase gene Gene Primer Sequence Hydantoinase 5′- CGCGAATTCCGAGAAGGAGCGCTGTCATGTTC SEQ ID NO: 11 side EcoRI Initiation codon 3- CGCGGATCCGATGCGATCGGCCCGCGCCTG SEQ ID NO: 12 side BamHI N-carbamyl- 5′- CGCGAATTCGCGAGAGGGAGGTGTCGTCATGA SEQ ID NO: 13 L-amino acid side CGCTG hydrolase EcoRI   Initiation codon 3- CGCGGATCCAACGTCACCGGTCAAGCGCCGTC SEQ ID NO: 14 side ACGA BamHI Termination codon 2. Preparation of a Cell-Free Extract

E. coli transformant harboring pUCHH and E. coli transformant harboring pUCCH were seeded and cultured at 37° C. for 16 hours in LB medium containing 0.1 mg/ml ampicillin. 1 ml of this seed culture liquid was added in a 500-ml Sakaguchi flask containing 50 ml LB medium, and then cultured at 37° C. In 2.5 hours after culture was initiated, isopropyl-1-thio-β-D-galactopyranoside (IPTG) was add thereto at a final concentration of 1 mM, and culture was further continued for 4 hours.

After the culture was finished, the microorganism was collected, washed, suspended in 5 ml of 50 mM KPB (pH 8.0) and disrupted with 0.1 mmφ glass beads for 3 minutes (30 seconds×6 times at 90-second intervals) with a beads beater. The solution was recovered and centrifuged at 20,000 g×10 minutes, and the supernatant was used as the cell-free extract.

3. Measurement of the Activities of Hydantoinase and N-Carbamyl-L-Amino Acid Hydrolase

For measurement of the hydantoinase activity, a reaction solution containing 120 mg/dl 5-benzyl hydantoin (BH; D-, L- and DL-hydantoin), 50 mM KPB (pH 8.0) and an enzyme solution was incubated at 37° C. for 30 minutes, then a 9-fold volume of 1.1 mM CuSO4 and 11.1 mM H3PO4 was added thereto and centrifuged at 20,000 g×10 minutes, to remove precipitates, and the formed N-carbamyl phenylalanine (N-Car-Phe) was quantified by HPLC to determine the hydantoinase activity. The enzyme activity causing formation of 1 μmol N-carbamyl phenylalanine per minute under these conditions was defined as 1 U of the enzyme activity.

For measurement of the N-carbamyl-L-amino acid hydrolase activity, a reaction solution containing 80 mg/dl N-carbamyl-L-phenylalanine, 50 mM KPB (pH 7.5) and an enzyme solution was incubated at 37° C. for 30 minutes, then a 9-fold volume of 1.1 mM CuSO4 and 11.1 mM H3PO4 was added thereto and centrifuged at 20,000 g×10 minutes, to remove precipitates, and the formed L-phenylalanine (L-Phe) was quantified by HPLC to determine the N-carbamyl-L-amino acid hydrolase activity. The enzyme activity causing formation of 1 μmol L-phenylalanine per minute under these conditions was defined as 1 U of the enzyme activity.

The HPLC conditions used in measurement of the two enzymes are as follows:

Column: Daicel Chemical Industries Ltd. CHIRALPAK WH 0.46 cmφ×25 cm

Mobile phase: 5% (v/v) methanol, 1 mM CuSO4

Column temperature: 50° C.

Flow rate: 1.5 ml/min.

Detection: UV210

The results are shown in Table 5. In the strain transformed with pUCHH, a hydantoinase activity was detected, and in the strain transformed with pUCCH, an N-carbamyl-L-amino acid hydrolase activity was detected, and it was thus confirmed that the two genes are the hydantoinase gene and the N-carbamyl-L-amino acid hydrolase gene respectively derived from Microbacterium liquefaciens AJ3912, and expressed in the E. coli microorganisms. With respect to the hydantoinase activity, D- and L-N-carbamyl phenylalanine was formed respectively in the presence of D- and L-5-benzyl hydantoin as the substrate, thus revealing that the enzyme could act both D- and L-amino acid.

TABLE 5 Enzyme activity of the cell-free extract of E. coli harboring pUCHH and pUCCH N-carbamyl-L- amino acid Addition Hydantoinase hydrolase Plasmid of IPTG activity (U/mg) activity (U/mg) pUCHH + DL 0.11 Not detected + D 0.10 Not detected + L 0.13 Not detected − DL 0.01 Not detected − D 0.01 Not detected − L 0.02 Not detected pUCHH + DL Not detected 0.10 − DL Not detected 0.01 pUC18 + DL Not detected Not detected − DL Not detected Not detected 4. Production of L-Phenylalanine from L-5-Benzyl Hydantoin

Out of the cell-free extracts described above, 0.01 ml each of IPTG-added extracts showing higher hydantoinase and N-carbamyl-L-amino acid hydrolase activities respectively, 0.5 g/dl L-5-benzyl hydantoin and 0.1 M KPB (pH 7.5) were subjected to stationary reaction at 30° C. The reaction solution was sampled with time, and a 9-fold volume of 1.1 mM CuSO4 and 11.1 mM H3PO4 was added thereto and centrifuged at 20,000 g×10 minutes, to remove precipitates, and the formed L-phenylalanine was quantified by HPLC.

The results are shown in Table 6. As shown in this table, L-phenylalanine could be formed efficiently from L-5-benzyl hydantoin by using the cell-free extracts prepared from the E. coli expressing the hydantoinase gene and N-carbamyl-L-amino acid hydrolase gene.

TABLE 6 Production of L-phenylalanine from L-5-benzyl hydantoin Reaction time L-BH N-Car-L-Phe L-Phe (hr) (g/dl) (g/dl) (g/dl) 0 0.50 0.00 0.00 5 0.31 0.12 0.05 12 0.15 0.11 0.22 24 0.00 0.01 0.42

Example 3 Production of L-Phenylalanine by Using the Washed E. coli Microorganism

0.5 g/dl (26 mM) L-5-benzyl hydantoin, 0.1 M KPB (pH 7.5), 1 g/dl washed microorganism of JM109/pUCHH, and 1 g/dl washed microorganism of JM109/pUCCH were mixed and reacted at 30° C. The reaction solution was sample with time, and its centrifuged supernatant was analyzed by HPLC, whereby the formed L-phenylalanine was quantified.

The results are shown in Table 7. As shown in this table, L-phenylalanine could be formed efficiently from L-5-benzyl hydantoin by using the washed microorganisms of E. coli expressing the hydantoinase gene and N-carbamyl-L-amino acid hydrolase gene respectively.

TABLE 7 Production of L-phenylalanine by the washed microorganisms of E. coli Reaction time L-BH N-Car-L-Phe L-Phe (hr) (g/dl) (g/dl) (g/dl) 0 0.50 0.00 0.00 5 0.39 0.04 0.05 12 0.22 0.05 0.19 24 0.07 0.04 0.32 36 0.00 0.00 0.41

Example 4 Production of 2-amino-6-methyl-6-nitroheptanoic Acid by the Washed Microorganism of E. coli

100 mg L-5-(4-methyl-4-nitropentyl) hydantoin (MNPH) was suspended in 16 ml of 100 mM Tris-HCl buffer (pH 8.0), and 2 ml washed microorganism of JM109/pUCHH and 2 ml washed microorganism of JM109/pUCCH were added thereto and reacted at 37° C. The reaction solution was sample with time, and its centrifuged supernatant was analyzed by HPLC, whereby the formed 2-amino-6-methyl-6-nitroheptanoic acid (AMNHA) was quantified. The results are shown in Table 8. The HPLC conditions are as follows:

Column: GL Science Inert Sil ODS-20.46 cmφ×25 cm Mobile phase: 30 mM aqueous phosphoric acid/methanol=8/2 (V/V)

Column temperature: 50° C.

Flow rate: 1.0 ml/min.

Detection: UV210 nm

TABLE 8 Production of 2-amino-6-methyl-6-nitroheptanoic acid by the washed microorganisms of E. coli Formed Remaining Reaction time AMNHA(g/dl) MNPH (g/dl) 0 0.00 0.50 10 0.13 0.33 24 0.25 0.14 48 0.36 0.00

After the reaction, the reaction solution was diluted with 200 ml water, and the microorganisms were removed by centrifugation (12,000×g, 10 minutes). Thereafter, the supernatant was applied onto a cation-exchange resin column (Amberlite IR-120b, 2.6 cmφ×20 cm) at a flow rate of 3 ml/min., whereby 2-amino-6-methyl-6-nitroheptanoic acid was adsorbed thereon. The column was washed with 500 ml water, and 300 ml of 2% ammonia water was passed at a rate of 3 ml/min. through the column, to eluate 2-amino-6-methyl-6-nitroheptanoic acid. The eluate was concentrated to a volume of 3 ml under reduced pressure in a rotary evaporator at 40° C., followed by dropwise addition of acetone to give 2-amino-6-methyl-6-nitroheptanoic acid as an ammonium salt (dry salt: 31 mg). The resultant 2-amino-6-methyl-6-nitroheptanoic acid was subjected to HPLC analysis by an optical resolution column. The analysis conditions are as follows:

Column: Daicel Chemical Industries Ltd. CROWNPAK CR (+) 4.6 cmφ×25 cm

Mobile phase: Aqueous perchloric acid (pH 1.8)/acetonitrile=8/2 (V/V)

Column temperature: 50° C.

Flow rate: 1.0 ml/min.

Detection: UV210 nm

Under these conditions, D-2-amino-6-methyl-6-nitroheptanoic acid and L-2-amino-6-methyl-6-nitroheptanoic acid can be fractionated and quantified at retention times of 4.2 and 6.1 minutes, respectively.

The result revealed that the 2-amino-6-methyl-6-nitroheptanoic acid formed in this reaction was in L-configuration, and its optical purity was 99% e.e. or more.

Example 5 Production of L-(3′-pyridyl)-Alanine by the Washed Microorganisms of E. coli

100 mg L-5-(3′-pyridyl)-methyl hydantoin was suspended in 16 ml of 100 mM Tris-HCl buffer (pH 8.0), and 2 ml washed microorganism of JM109/pUCHH and 2 ml washed microorganism of JM109/pUCCH were added thereto and reacted at 37° C. for 48 hours. The reaction solution was centrifuged, and the supernatant was analyzed by HPLC, whereby the formed 3′-pyridyl-alanine was quantified. The HPLC conditions are as follows:

Column: Daicel Chemical Industries Ltd. CROWNPAK CR (+) 4.6 cmφ×25 cm

Mobile phase: Aqueous perchloric acid (pH 1.5)

Column temperature: 15° C.

Flow rate: 0.75 ml/min.

Detection: UV210 nm

Under these conditions, D-(3′-pyridyl)-alanine and L-(3′-pyridyl)-alanine can be fractionated and quantified at retention times of 2.0 and 2.3 minutes, respectively.

The result revealed that 3′-pyridyl-alanine formed in this reaction was in L-configuration, and its optical purity was 99% e.e. or more. The amount of L-(3′-pyridyl)-alanine formed was 0.4 g/dl.

Example 6 Production of L-Amino Acids by the Washed Microorganisms of E. coli

Various 5-substituted hydantoin compounds, 1 g/dl washed microorganism of JM109/pUCHH and 1 g/dl washed microorganism of JM109/pUCCH were mixed and reacted at 30° C. in the same manner as above in production of L-phenylalanine. After 24 hours, the reaction solution was sampled, and its centrifuged supernatant was analyzed by HPLC, whereby the formed L-amino acids were quantified.

The results are shown in Table 9. As shown in this table, L-amino acids could be formed efficiently from various 5-substituted hydantoin compounds by using the washed microorganisms of E. coli expressing the hydantoinase gene and N-carbamyl-L-amino acid hydrolase gene respectively.

TABLE 9 Production of L-amino acids by the washed microorganisms of E. coli Amount of amino acid 5-Substituted hydantoin formed compound Formed amino acid (g/dl) L-5-benzyl hydantoin L-phenylalanine 0.32 L-5-(4-hydroxybenzyl) L-tyrosine 0.30 hydantoin L-5-indolyl methyl L-tryptophan 0.41 hydantoin L-5-(3, 4-dihydroxy benzyl) L-3, 4-dihydroxy 0.34 hydantoin phenylalanine L-5-methyl thioethyl L-methionine 0.03 hydantoin

According to the present invention, the hydantoinase gene and N-carbamyl-L-amino acid hydrolase gene could be expressed stably in a large amount in a host such as colon bacteria. As a result, the enzymes could be easily prepared from such a transformant, and by using the transformant or its extract, or the purified enzymes etc., optically active amino acids useful for production of pharmaceutical preparations, products in chemical industry, food additives etc. could be efficiently produced.

INDUSTRIAL APPLICABILITY

As described above, the DNA encoding hydantoinase, the DNA encoding N-carbamyl-L-amino acid hydrolase, the recombinant DNA, the transformed cells, the method of producing a protein and the method of producing optically active amino acids according to the present invention are useful in fields related to production of optically active amino acids and used preferably in fields such as pharmaceutical preparations, products in chemical industry, food additives etc. 

The invention claimed is:
 1. An isolated DNA encoding for a protein having an N-carbamyl-L-amino acid hydrolase activity, which has the nucleotide sequence of SEQ ID NO:3.
 2. A recombinant DNA obtained by linking the DNA according to claim 1 to a vector DNA.
 3. The recombinant DNA according to claim 2, wherein the vector DNA is a pUC series plasmid, or a pBR322 plasmid.
 4. A cell transformed with the recombinant DNA according to claim
 2. 5. A cell according to claim 4, wherein said cell is Escherichia coli.
 6. A method of producing a protein having an N-carbamyl-L-amino acid hydrolase activity, wherein the cell according to claim 4 is cultured in a medium, and a protein having an N-carbamyl-L-amino acid hydrolase activity is accumulated in the medium and/or the cells.
 7. A method of producing an L-amino acid, comprising: producing a protein having an N-carbamyl-L-amino acid hydrolase activity by the method according to claim 6; and contacting N-carbamyl-L-amino acid with the protein having an N-carbamyl-L-amino acid hydrolase activity.
 8. A method of producing an L-amino acid, comprising: producing a protein having an N-carbamyl-L-amino acid hydrolase activity by the method according to claim 6; and converting 5-substituted hydantoin to an L-amino acid in the presence of the protein having an N-carbamyl-L-amino acid hydrolase activity and an enzyme hydrolyzing 5-substituted hydantoin or a material containing the enzyme.
 9. A method of producing an L-amino acid, comprising: producing a first protein having a hydantoinase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA encoding for a protein having a hydantoinase activity, which has the following nucleotide sequence (c): (c) the nucleotide sequence of SEQ ID NO:1, to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a hydantoinase activity is accumulated in any one or both of the medium and the cells; producing a second protein having an N-carbamyl-L-amino acid hydrolase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA according to claim 1 to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a N-carbamyl-L-amino acid hydrolase activity is accumulated in any one or both of the medium and the cells; and producing an L-amino acid by converting 5-substituted hydantoin to an L-amino acid in the presence of the protein having a hydantoinase activity and the protein having an N-carbamyl-L-amino acid hydrolase activity.
 10. A method of producing an L-amino acid, comprising: producing a first protein having a hydantoinase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA encoding for a protein having a hydantoinase activity, which has the following amino acid sequence (c) or (d): (c) the amino acid sequence of SEQ ID NO:2, and (d) an amino acid sequence wherein in the amino acid sequence of SEQ ID NO:2, one to ten amino acid residues are replaced, deleted, inserted, or added, to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a hydantoinase activity is accumulated in any one or both of the medium and the cells; producing a second protein having an N-carbamyl-L-amino acid hydrolase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA according to claim 1 to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a N-carbamyl-L-amino acid hydrolase activity is accumulated in any one or both of the medium and the cells; and producing an L-amino acid by converting 5-substituted hydantoin to an L-amino acid in the presence of the protein having a hydantoinase activity and the protein having an N-carbamyl-L-amino acid hydrolase activity.
 11. A method of producing L-tyrosine, comprising: producing a protein having a hydantoinase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA encoding for a protein having a hydantoinase activity, which has the following nucleotide sequence (c): (c) the nucleotide sequence of SEQ ID NO:1, to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a hydantoinase activity is accumulated in any one or both of the medium and the cells; producing a second protein having an N-carbamyl-L-amino acid hydrolase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA according to claim 1 to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a N-carbamyl-L-amino acid hydrolase activity is accumulated in any one or both of the medium and the cells; and producing L-tyrosine by converting DL-5-(4-hydroxybenzyl) hydantoin to L-tyrosine in the presence of the protein having a hydantoinase activity and the protein having an N-carbamyl-L-amino acid hydrolase activity.
 12. A method of producing L-tyrosine, comprising: producing a first protein having a hydantoinase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA encoding for a protein having a hydantoinase activity, which has the following amino acid sequence (c) or (d): (c) the amino acid sequence of SEQ ID NO:2, and (d) an amino acid sequence wherein in the amino acid sequence of SEQ ID NO:2, one to ten amino acid residues are replaced, deleted, inserted, or added, to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a hydantoinase activity is accumulated in any one or both of the medium and the cells; producing a second protein having an N-carbamyl-L-amino acid hydrolase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA according to claim 1 to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a N-carbamyl-L-amino acid hydrolase activity is accumulated in any one or both of the medium and the cells; and producing L-tyrosine by converting DL-5-(4-hydroxybenzyl) hydantoin to L-tyrosine in the presence of the protein having a hydantoinase activity and the protein having an N-carbamyl-L-amino acid hydrolase activity.
 13. An isolated DNA encoding for a protein having an N-carbamyl-L-amino acid hydrolase activity and having the following amino acid sequence (c) or (d): (c) the amino acid sequence of SEQ ID NO:4, and (d) an amino acid sequence wherein in the amino acid sequence of SEQ ID NO:4, one to ten amino acid residues are replaced, deleted, inserted, or added.
 14. A recombinant DNA obtained by linking the DNA according to claim 13 to a vector DNA.
 15. The recombinant DNA according to claim 14, wherein the vector DNA is a pUC series plasmid, or a pBR322 plasmid.
 16. A cell transformed with the recombinant DNA according to claim
 14. 17. A cell according to claim 16, wherein said cell is Escherichia coli.
 18. A method of producing a protein having an N-carbamyl-L-amino acid hydrolase activity, wherein the cell according to claim 16 is cultured in a medium, and a protein having an N-carbamyl-L-amino acid hydrolase activity is accumulated in the medium and/or the cells.
 19. A method of producing an L-amino acid, comprising: producing a protein having an N-carbamyl-L-amino acid hydrolase activity by the method according to claim 18; and contacting N-carbamyl-L-amino acid with the protein having an N-carbamyl-L-amino acid hydrolase activity.
 20. A method of producing an L-amino acid, comprising: producing a protein having an N-carbamyl-L-amino acid hydrolase activity by the method according to claim 18; and converting 5-substituted hydantoin to an L-amino acid in the presence of the protein having an N-carbamyl-L-amino acid hydrolase activity and an enzyme hydrolyzing 5-substituted hydantoin or a material containing the enzyme.
 21. A method of producing an L-amino acid, comprising: producing a first protein having a hydantoinase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA encoding for a protein having a hydantoinase activity, which has the following nucleotide sequence (a): (a) the nucleotide sequence of SEQ ID NO:1, to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a hydantoinase activity is accumulated in any one or both of the medium and the cells; producing a second protein having an N-carbamyl-L-amino acid hydrolase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA according to claim 13 to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a N-carbamyl-L-amino acid hydrolase activity is accumulated in any one or both of the medium and the cells; and producing an L-amino acid by converting 5-substituted hydantoin to an L-amino acid in the presence of the protein having a hydantoinase activity and the protein having an N-carbamyl-L-amino acid hydrolase activity.
 22. A method of producing an L-amino acid, comprising: producing a first protein having a hydantoinase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA encoding for a protein having a hydantoinase activity, which has the following amino acid sequence (a) or (b): (a) the amino acid sequence of SEQ ID NO:2, and (b) an amino acid sequence wherein in the amino acid sequence of SEQ ID NO:2, one to ten amino acid residues are replaced, deleted, inserted, or added, to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a hydantoinase activity is accumulated in any one or both of the medium and the cells; producing a second protein having an N-carbamyl-L-amino acid hydrolase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA according to claim 13 to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a N-carbamyl-L-amino acid hydrolase activity is accumulated in any one or both of the medium and the cells; and producing an L-amino acid by converting 5-substituted hydantoin to an L-amino acid in the presence of the protein having a hydantoinase activity and the protein having an N-carbamyl-L-amino acid hydrolase activity.
 23. A method of producing L-tyrosine, comprising: producing a protein having a hydantoinase activity wherein a cell of Escherichia coli-transformed with the recombinant DNA obtained by linking a DNA encoding for a protein having a hydantoinase activity, which has the following nucleotide sequence (a): (a) the nucleotide sequence of SEQ ID NO:1, to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a hydantoinase activity is accumulated in any one or both of the medium and the cells; producing a second protein having an N-carbamyl-L-amino acid hydrolase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA according to claim 13 to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a N-carbamyl-L-amino acid hydrolase activity is accumulated in any one or both of the medium and the cells; and producing L-tyrosine by converting DL-5-(4-hydroxybenzyl) hydantoin to L-tyrosine in the presence of the protein having a hydantoinase activity and the protein having an N-carbamyl-L-amino acid hydrolase activity.
 24. A method of producing L-tyrosine, comprising: producing a first protein having a hydantoinase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA encoding for a protein having a hydantoinase activity, which has the following amino acid sequence (a) or (b): (a) the amino acid sequence of SEQ ID NO:2, and (b) an amino acid sequence wherein in the amino acid sequence of SEQ ID NO:2, one to ten amino acid residues are replaced, deleted, inserted, or added, to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a hydantoinase activity is accumulated in any one or both of the medium and the cells; producing a second protein having an N-carbamyl-L-amino acid hydrolase activity wherein a cell of Escherichia coli transformed with the recombinant DNA obtained by linking a DNA according to claim 13 to a vector DNA selected from the group consisting of a pUC series plasmid, and a pBR322 plasmid is cultured in a medium and a protein having a N-carbamyl-L-amino acid hydrolase activity is accumulated in any one or both of the medium and the cells; and producing L-tyrosine by converting DL-5-(4-hydroxybenzyl) hydantoin to L-tyrosine in the presence of the protein having a hydantoinase activity and the protein having an N-carbamyl-L-amino acid hydrolase activity. 